Organization - Additional Information (Detail)
$ / shares in Units, ft² in Millions
 9 Months Ended
Nov. 10, 2020
ft²
StorageFacility
State
StorageUnit
RealEstateVenture
$ / shares
Apr. 20, 2020
$ / shares
Oct. 29, 2019
USD ($)
Jan. 09, 2017
USD ($)
shares
May 23, 2014
USD ($)
Aug. 02, 2013
USD ($)
Sep. 30, 2020
USD ($)
StorageFacility
State
$ / shares
shares
Oct. 26, 2020
USD ($)
May 14, 2020
$ / shares
Dec. 31, 2019
$ / shares
shares
Oct. 01, 2018
State
Nov. 30, 2016
shares
Organization And Nature Of Operations [Line Items]                        
Date of formation of company             Jan. 08, 2013          
Number of self storage facilities | StorageFacility             112          
Number of states located for self storage facilities | State             17       10  
Shares issuable pursuant to distribution reinvestment plan             $ 95,000,000.0          
Maximum purchase commitment amount     $ 200,000,000                  
Initial closing amount     $ 150,000,000                  
Preferred stock, dividend rate, percentage     6.25%                  
Advisor, SS Toronto REIT Advisors, Inc., and SS Growth Advisor, LLC.                        
Organization And Nature Of Operations [Line Items]                        
Percentage of limited partnership interests             86.50%          
SAM and Affiliates                        
Organization And Nature Of Operations [Line Items]                        
Percentage of limited partnership interests owned by noncontrolling owners             13.50%          
Fifth To Tenth Anniversary                        
Organization And Nature Of Operations [Line Items]                        
Dividend rate percentage of increase on preferred stock     0.75%                  
After Tenth Anniversary                        
Organization And Nature Of Operations [Line Items]                        
Dividend rate percentage of increase on preferred stock     0.75%                  
Distribution Reinvestment Plan                        
Organization And Nature Of Operations [Line Items]                        
Common Stock, shares authorize | shares                       100,900,000
Description for termination of offering             The DRP Offering may be terminated at any time upon 10 days’ prior written notice to stockholders.          
Preferred Stock                        
Organization And Nature Of Operations [Line Items]                        
Preferred Stock, shares authorize | shares             200,000,000     200,000,000    
Preferred Stock, par value | $ / shares             $ 0.001     $ 0.001    
Maximum | Tenth Anniversary                        
Organization And Nature Of Operations [Line Items]                        
Preferred stock, dividend rate, percentage     9.00%                  
Primary Offering | Maximum                        
Organization And Nature Of Operations [Line Items]                        
Common stock, value authorize             $ 1,000,000,000.0          
Primary Offering | Minimum                        
Organization And Nature Of Operations [Line Items]                        
Sale of common shares         $ 1,500,000              
Class A Common stock                        
Organization And Nature Of Operations [Line Items]                        
Common Stock, shares authorize | shares             350,000,000     350,000,000    
Common Stock, par value | $ / shares             $ 0.001     $ 0.001    
Estimated value per common share | $ / shares   $ 10.40                    
Class A Common stock | Distribution Reinvestment Plan                        
Organization And Nature Of Operations [Line Items]                        
Selling price per share | $ / shares                 $ 10.40      
Class A Common stock | Common Stock | Distribution Reinvestment Plan                        
Organization And Nature Of Operations [Line Items]                        
Gross proceeds from issuance of common stock             $ 52,100,000          
Number of common stock issued | shares             5,000,000.0          
Class A Common stock | Primary Offering | Common Stock                        
Organization And Nature Of Operations [Line Items]                        
Number of shares issued in offering | shares       48,000,000                
Gross proceeds from issuance of common stock       $ 493,000,000                
Class T Common stock                        
Organization And Nature Of Operations [Line Items]                        
Common Stock, shares authorize | shares             350,000,000     350,000,000    
Common Stock, par value | $ / shares             $ 0.001     $ 0.001    
Estimated value per common share | $ / shares   $ 10.40                    
Class T Common stock | Distribution Reinvestment Plan                        
Organization And Nature Of Operations [Line Items]                        
Selling price per share | $ / shares                 $ 10.40      
Class T Common stock | Common Stock | Distribution Reinvestment Plan                        
Organization And Nature Of Operations [Line Items]                        
Gross proceeds from issuance of common stock             $ 8,000,000.0          
Number of common stock issued | shares             800,000          
Class T Common stock | Primary Offering | Common Stock                        
Organization And Nature Of Operations [Line Items]                        
Number of shares issued in offering | shares       7,000,000                
Gross proceeds from issuance of common stock       $ 73,000,000                
Series A Convertible Preferred Stock                        
Organization And Nature Of Operations [Line Items]                        
Preferred Stock, shares authorize | shares             200,000     200,000    
Preferred Stock, par value | $ / shares             $ 0.001     $ 0.001    
Subsequent Event                        
Organization And Nature Of Operations [Line Items]                        
Second and final closing amount               $ 50,000,000        
Subsequent Event | SST IV Merger Agreement                        
Organization And Nature Of Operations [Line Items]                        
Number of self storage facilities | StorageFacility 24                      
Number of states located for self storage facilities | State 9                      
Number of self storage units | StorageUnit 18,000                      
Net rentable area, primarily self storage space | ft² 2.0                      
Subsequent Event | SST IV Merger Agreement | Class A Common stock                        
Organization And Nature Of Operations [Line Items]                        
Common Stock, par value | $ / shares $ 0.001                      
Subsequent Event | SST IV Merger Agreement | Canada                        
Organization And Nature Of Operations [Line Items]                        
Percentage of voting membership interest 50.00%                      
Number of unconsolidated real estate ventures | RealEstateVenture 5                      
SmartStop Self Storage, Inc.                        
Organization And Nature Of Operations [Line Items]                        
Number of self storage professionals and other personnel | StorageFacility             350          
Strategic Storage Operating Partnership II, L.P.                        
Organization And Nature Of Operations [Line Items]                        
Date of formation of company             Jan. 09, 2013          
Advisor purchased a limited partnership interest in Operating Partnership           $ 200,000            
Initial capital contribution           $ 1,000            
SmartStop Asset Management                        
Organization And Nature Of Operations [Line Items]                        
Percentage of non-voting equity owned             15.00%          
SmartStop Asset Management | Investments in Majority-owned Subsidiaries                        
Organization And Nature Of Operations [Line Items]                        
Percentage of non-voting equity owned             15.00%          
Self Administration Transaction | Strategic Storage Property Management II, LLC                        
Organization And Nature Of Operations [Line Items]                        
Percentage of voting membership interest             100.00%          
Self Administration Transaction | SS Growth Property Management, LLC                        
Organization And Nature Of Operations [Line Items]                        
Percentage of voting membership interest             100.00%          
Self Administration Transaction | Strategic Storage Advisor II, LLC                        
Organization And Nature Of Operations [Line Items]                        
Percentage of voting membership interest             100.00%